1. Field of the Invention
The present invention relates to the art of controlling current and power to alternating current induction motors, and more particularly relates to the control of the firing sequence of the stator pole coil for minimizing linkage power differences, and for maximizing the flux linkage between the coils of the stator and the rotor to maximize energy efficiency.
2. Description of the Prior Art
In the past, alternating current (AC) induction motors were constructed having a plurality of poles arranged in a circumference on the stator around a corresponding plurality of poles arranged on a rotor. As the coils of the poles of the stator have their corresponding electromagnetic fluxes changed by a change of the current in the coil, the attractive and repulsive forces against the sympathetic poles of the rotor force the rotor to move. When the change in the electromagnetic flux polarity of the stator poles changes sequentially, in the circumferential or peripheral direction, the rotor rotates in the desired direction. Obviously, the timing of the current change in the coils is important to maintain the momentum, acceleration or deceleration of the rotor's rotation. AC induction motors have used for such timing a source of clocking pulses and an oscillator generating a firing frequency or pulse train.
In the past, the frequency generated by the oscillator maintained a constant phase and was used as the basis of the clock. The frequency thus served as an immutable reference in the system. The unchanging nature of the generated frequency, however, does not help maintain the maximum efficiency between the stator and the rotor as the speed is increased or decreased. As the frequency is decreased in order to decrease speed of rotation, the firing sequence of systems of the past, is maintained at the clock frequency. The decreased frequency then places an increased load on the flux linkage and on the stator coils as the rotor slips behind in the flux linkage scheme.
This increased load creates an inefficiency in the energy supplied-to-energy derived ratio. There is a power reduction in the rotor's output which is not seen comparatively in the electrical power input.